The present invention relates to a print head for an inkjet printer which utilizes n interlacing passes. The print head is provided with a plurality of regular nozzles disposed in a row, the row having a first end and a second end, each defined by an associated regular nozzle. Neighboring regular nozzles are positioned from one another at a distance of a regular nozzle pitch N, where N=n*ds, ds being the dot pitch (the distance between two drops on a paper). A reserve nozzle is located at a distance from at least one of the ends of the row of nozzles, thus providing an extension of the row of nozzles.
The present invention also relates to a method of printing an image built up from a number of sub-images.
A print head is known from EP-A-0 783 973. In this known print head, the number of interlacing passes required is 1, so that n=1 and the dot pitch ds is equal to the regular nozzle pitch N. The distance between the reserve nozzle and the end is also a multiple of the regular nozzle pitch. In this method, the print head is moved from a starting position over an xe2x80x9coutgoing passxe2x80x9d and thus an image is printed by properly operating the regular nozzles. The nozzle which is not operative is recorded. The print head is then displaced over one or more nozzle pitches in a direction perpendicular to the outgoing pass so that a properly operating nozzle comes into the position of a non-printed line caused by a defective nozzle. The non-printed line from the xe2x80x9coutgoingxe2x80x9d pass is then printed during the movement of the print head in the opposite direction to the outgoing pass, that is, on the xe2x80x9creturnxe2x80x9d pass, with the associated properly operating regular nozzle. The other nozzles are not activated on this return pass. Finally the print head is moved back in a direction perpendicular to the outgoing pass into the original starting position and the print head is moved up over a xe2x80x9cswathxe2x80x9d length, i.e. over the complete length of the row of regular nozzles, in a direction perpendicular to the outgoing and return pass into a new starting position. The printing of lines which have not been printed due to a defective nozzle, using this known method, has the disadvantage of a loss of productivity. Also, a separate printing pass is required to fill in a non-printed line due to a defective nozzle. Only the missing line is printed in this printing pass. Print heads are also known with an interlacing pass n greater than 1.
It is the object of the present invention to provide a print head with an interlacing pass n greater than 1 wherein the loss of productivity due to the printing of A missing line due to a defective nozzle is considerably reduced.
To this end, a print head of the type described above is provided, wherein the number of interlacing passes required, n, is larger than 1 (n greater than 1) and the distance 10 between the reserve nozzle and the associated end of the row is I*ds, where I is an integer and is not equal to (p/k)*n, where p is an integer, and k is an integer smaller than n. Since interlacing is effected, an image is built up from different sub-images, the number of sub-images being equal to n. When the distance satisfies this condition, the reserve nozzle is not situated at a distance of a multiple of the regular nozzle pitch from the end. Consequently, on displacement of the reserve nozzle to the position of a missing line, in order to fill in the line in a following pass, the regular nozzles being disposed in a following pass at locations of lines which have already been filled in is avoided.
In a preferred embodiment of a print head according to the present invention, the loss of productivity is further reduced by disposing a reserve nozzle at both ends.
In still another embodiment of the print head of the present invention, the latter is provided with a plurality of reserve nozzles at one end.
In particular, print heads are used for ink jet printers with an interlacing pass of n=4. In these conditions therefore I can be odd, while in order to avoid making the print head too large I is kept low.
The present invention further applies to a method of printing an image built up from a number of sub-images, wherein neighboring sub-images are spaced apart by a dot pitch ds, in which a print head is used in accordance with the invention, said method comprising the steps of:
performing a number of printing passes of the print head to form the number of sub-images,
detecting the position of a defective regular nozzle before and during a first printing pass respectively, and
displacing the print head over a distance between a preceding and a following printing pass such that the reserve nozzle, during the following printing pass, comes into the position occupied by the defective nozzle in the preceding printing pass. As a result, on a subsequent printing pass, not only the missing line due to the defective nozzle can be filled in by the reserve nozzle, but also a following sub-image is printed by the properly operating regular nozzles. The properly operating regular nozzles are situated on lines which have not yet been printed, as a result of the inventive choice of the distance of the reserve nozzle from the end of the row of regular nozzles.
In a preferred embodiment of the method according to the present invention, a grid of eight sub-images is made with an interlacing pass n=4, and a first reserve nozzle and a second reserve nozzle are used, wherein an extra pass, sub-image number 9, is made during which both reserve nozzles print simultaneously in such manner that no blank line continues to remain in the grid due to a defective nozzle. With this method, a first series of four sub-images is first printed. The print head then shifts over a print head length and a second series of four sub-images is printed. The two blank lines finally remaining in these conditions due to the defective nozzle are printed in the extra pass, i.e., sub-image No. 9. This method is for use on print heads with an arbitrary interlacing pass n, by performing the extra pass after the nth printing pass, only the first and second reserve nozzles printing in this case.